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UGH, just spent WAAAY too much time debugging this bug myself while upgrading some code to ruby 1.9.

As a note for those using rspec < 2.6, a workaround is to use the syck YAML parser instead of psych, which is a new default in ruby 1.9. If you can upgrade your rspec version, that's definitely the best way, as syck has issues of its own.